We plan to determine the number of antibody molecules of different classes that are needed to induce immunologic enhancement or to cause antibody-mediated suppression of tumor growth. The mechanisms of immunologic enhancement induced by different classes of antibodies will be compared. The type of effector cells that are active with each class of antibody in antibody-mediated suppression of tumor growth in vivo will be identified. In a cell culture system, the class of antibody that can suppress the immune response to various antigens will be identified, the effectiveness of suppression on a per antibody molecule basis determined and the mechanisms of suppression studied. Also the mechanisms of in vitro antibody-dependent macrophage-mediated and platelet-mediated target cell destruction will be studied. The in vivo significance of antibody-dependent platelet-mediated tumor cell destruction will be evaluated in a guinea pig leukemia model.